MAX7060ATG/V+ Maxim Integrated Products, MAX7060ATG/V+ Datasheet - Page 14

• Manufacturer Part Number: MAX7060ATG/V+
• Description: RF Transmitter 300MHz to 450MHz Fre quency-and-Output-Po
• Manufacturer: Maxim Integrated Products

Specifications of MAX7060ATG/V+

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

280MHz to 450MHz Programmable
ASK/FSK Transmitter
pins. Connecting PAVOUT to PAOUT enables Tx power
control. In SPI mode, there are 31 power-control settings
in approximately 1dB monotonic steps. In manual mode,
four power-control settings are available.
The MAX7060 has two types of ASK envelope shaping:
digital shaping (SPI mode only) and analog shaping
through an internal resistor. Envelope shaping results
in a smaller spectral width of the modulated PA output
signal.
In digital shaping, the user can choose the final Tx power
setting, the power step size in units as small as 1dB, and
the step-time interval in units as small as 0.25Fs, when a
16MHz crystal is used. This shaping method causes the
PA to transmit an envelope that rises linearly in decibels
(exponentially in power) with time. Digital shaping is pro-
grammed through the SPI.
The analog shaping mode uses an internal envelope-
shaping resistor for ASK modulation, which connects
between PAVOUT and ROUT. When connected to the
PA pullup inductor, the envelope-shaping resistor slows
the turn-on/turn-off time of the PA. The user can choose
three turn-on/turn-off times through the SPI. A single turn-
on/turn-off time is set internally in manual mode.
The MAX7060 has an internal set of capacitors that can
be switched in and out to present different capacitor
values at the PA output. The capacitors are connected
from the PA output to ground. This allows changing the
tuning network along with the synthesizer divide ratio
each time the transmitted frequency changes, making
it possible to maintain maximum transmitter power while
moving rapidly from one frequency to another.
In SPI mode, the variable capacitor is programmed
through a register setting. In manual mode, the capacitor
setting is programmed through the DIN pin.
The tuning capacitor has a nominal resolution of 0.25pF,
from 0 to 7.75pF.
The MAX7060 utilizes a fully integrated fractional-N
PLL for its frequency synthesizer. All PLL components,
including the loop filter, are included on-chip. Two loop
bandwidths can be selected in SPI mode. The synthe-
sizer has 16-bit fractional-N topology (4 bits integer, 12
bits fractional) with a divide ratio that can be set from 19
to 28, allowing the transmit frequency to be adjusted in
increments of f
14
_____________________________________________________________________________________
XTAL
/4096.
Phase-Locked Loop (PLL)
ASK Envelope Shaping
Variable Capacitor
The fractional-N architecture also allows exact FSK
frequency deviations to be programmed, completely
eliminating the problems associated with generating fre-
quency deviations by crystal oscillator pulling.
FSK deviations as low as Q2kHz and as high as Q100kHz
can be set in SPI mode. In manual mode, the user can
select between Q16kHz and Q50kHz.
The integer and fractional portions of the PLL divider
ratio set the transmit frequency. This is done by load-
ing the divide-ratio registers in SPI mode, or selecting
the states of the three frequency-control pins (FREQ2,
FREQ1, FREQ0) in manual mode. For ASK modulation,
the two 8-bit center-frequency registers (fce[15:0]) are
loaded with the divide ratio determined by the center
frequency and the crystal. For FSK modulation, the two
8-bit high (mark) frequency registers (fhi[15:0]) and the
two 8-bit low (space) frequency registers (flo[15:0]) are
loaded. The divide ratios for the fhi and flo are deter-
mined by the center frequency, the frequency deviation,
and the crystal frequency. Examples of typical settings
for ASK and FSK modulation are given in the SPI Mode
Settings section.
The XTAL oscillator in the MAX7060 is designed to pres-
ent a capacitance of approximately 6pF between the
XTAL1 and XTAL2 pins. In most cases, this corresponds
to a 8pF load capacitance applied to the external crystal
when typical PCB parasitics are added. It is very impor-
tant to use a crystal with a load capacitance equal to the
capacitance of the MAX7060 crystal oscillator plus PCB
parasitics. If a crystal designed to oscillate with a differ-
ent load capacitance is used, the crystal is pulled away
from its stated operating frequency, introducing an error
in the reference frequency. A crystal designed to oper-
ate at a higher load capacitance than the value specified
for the oscillator is always pulled higher in frequency.
Adding capacitance to increase the load capacitance
on the crystal increases the startup time and can prevent
oscillation altogether.
In actuality, the oscillator pulls every crystal. The crystal’s
natural frequency is really below its specified frequency,
but when loaded with the specified load capacitance,
the crystal is pulled and oscillates at its specified fre-
quency. This pulling is already accounted for in the
specification of the load capacitance.
Crystal (XTAL) Oscillator